Tennis ball and the like and the manufacture thereof



y 1930. A. E. PENFOLD 1,771,861

TENNIS BALL AND THE LIKE AND THE MANUFACTURE THEREOF Filed Dec. 6, 19,24 2 Sheets-Sheet l avwzmtoz 4A 55/? 7 fA /Vgs r PIA F04 0 351 fuls Gum mm;

July 29, 1930. A. E. PENFOLD 1,771,861

TENNIS BALL AND THE LIKE AND THE MANUFACTURE THEREOF Filed 1924 2 Sheets-Sheet 2 anvemtoz 4455/? rim 5 r I EA FOL 0 3391 Zia J aren July 2a,. was

ALBERT ERNEST rnnronn, or BIRMINGHAM ENGLAND, essrenonro Dunner 'rmn AND nunnna ooaronarron or amnnreaorrurnnno, NEW YORK, A. conrona- 11011 on new roan TENNIS BALL AND THE LIKE AN D THE MANUFACTURE THEREOF application filed December 6, 1924:, Serial No. 754,263, and in Great Britain March 13, 1924.

such as felt which is adapted to resist wear.

and at the same time provide a surface by which the desired grip may be obtained upon the ball when struck by a tennis racquet.

To constitute a satisfactory ball it is essential that the inner core or foundation shall be free from porosity and absolutely gastight, but it has been found in practice to be extremely difficult and indeed impossible to avoid the production of large numbers of leaky and therefore defective balls by the use of the materials and methods of manufacture hitherto employed.

Such inner cores or foundations have hitherto been usually constructed of three shaped pieces ofhighly pigmented sheet rubber containing in some instances as much as 7 5% of solid matter,.each of the three piecesbeingbevelled at its edges by skilled operatives before they are joined to form an approximately spherical core or gas container. The jointing of the first two shaped pieces is not very difficult although it calls for extreme cleanliness and care, but the application of the third piece is more dificult especially in the final. sealing of the aperture after gas forming material has been placed within the core or retainer, and it has been customary to inspect the joint inside the core or gas retainer and for this purpose to use a small electric torch to give a good light.

Most of the difiiculties of jointing are due to extreme flexibility of the material heretofore used in the construction of the inner spherical core or gas container. Porosity is caused by the slightest defect in jointing and is also due to the pigments which are mixed with the rubber, and it is also due to ineflective sealing of the aperture through which gas is placed within the container by well known means, such as a hypodermic needle.

Gas for the initial inflation, is, however, in some cases produced from gas forming materials placed within the container before it is finally sealed during the subsequent vulcanization, which, however, are not intended to for a tennis ball and must be scrapped. And 7 should it be found that any of the joints are weak and porous so that the container cannot be inflated to extend to the surface of the mould, it is also useless.

The next step in the process is to inflate the core or container to the size and pressure requiredto produce a tennis ball conforming to limits specified by the tennis association. In practice the manufacturer inflates to slightly more than the correct diameter. The inflated containers are then put into stock and allowed to stand for a period.- of several months. After a given period they are tested for size and pressure and those which have leaked to such an extent that their size and pressure are less than those specified are put aside andsold at very low prices, being classified as unfit for tennis balls. Those passed as correct as regards size and pressure are issued for felt covering, and those still above the regulation size are put back for a further period. The lossof inflation pressure is due to one or more of three causes 1. Porosity of the highly pigmented compound.

2. Weak joints.

3. Plug leakage.

It sometimes occurs that whole batches of balls prove faulty, as many as 50% proving useless, with the risk of the remainder prov: ing leaky after they are covered with felt and issued for sale to the public. Such faults as I have referred to are defects discovered in manufacture, but it is well known that tennis balls as manufactured today cannot be stocked for more than a few months before they lose their resiliency and are unfit for use by expert exponents of the game.

It has been proposed to manufacture a tennis ball comprising two hemispherical cups composed of highly pigmented rubber compound, but this method is open to the same objections as the three piece method excepting that no plug is used, the gas being generated within the core. The troubles due to faulty plugs are, therefore, avoided, but when the container is built up of highly pigmented rubber under high gas pressure the joint around the seam which unites the two cups is not so positive. The defects are considerably greater than those experienced with the three piece process, and balls so constructed lose their inflation pressure in the same manner.

The objects of this invention are to overcome these defects and to produce tennis balls and similar balls having a gas content, which shall be non-porous and retain their inflation pressure, by the use of improved materials and an improved process by which accuracy of manufacture and absence of porosity may be ensured and at the same time the necessity for the-employment of highly skilled operatives will be obviated.

In carrying my invention into practice I build up or construct the inner core or spherical gas container of a ball of the type de scribed of two or more component parts composed of non-porous material, joined and sealed with an air-tight joint. For ease and accuracy of manipulation I prefer that such component parts should also be of a semirigid character. A suitable material from which to form such component parts having the characteristics of non-porosity and semirigidity is obtained from gutta percha or balata or a rubber mixture containing a proportion of gutta percha and/or balata. Such component parts are preferably moulded in the desired sizes and shapes and preferably they are suitably marked to ensure accuracy of joining and sealing and the formation of gas tight seams.

Inflation gas may be inserted intog the jointed container after it is moulded and 'vulcanized, and'in which case a plug composed of uncurable rubber is secured to the interior surface of one of the component parts of the container before the latter is completely joined in spherical form. In this case the nature of the material of which it is composed, and the greater accuracy of jointing secured by the greater rigidity of the component parts will ensure the absence of po-' while the container is vulcanized in a mould. The said mould being closed prevents overexpansion of the gas during vulcanization, and is allowed to cool before the moulded and vulcanized container is withdrawn therefrom, thus obviating subsequent over-expansion under the influence of heat.

The process of vulcanization in a restraining mould eliminates all irregularities in the configuration of the exterior surface of the container, such for example, as those at the joints or seams. It will, moreover, cause the container to lose its semi-rigidity and become more elastic and, under the influence of the inflation gases, exceedingly resilient. The said gas container may be coated with a covering of rubber when desired either before or after vulcanization, after which it may be provided with a covering of felt or other suitable material applied in any convenient manner.

In the accompanying drawings, I have shown how my invention may be conveniently and advantageously carried into practice in the manufacture of one ball of the type described, a tennis ball.

Referring to the drawings, Fig. l illustrates two semi-rigid hemispherical cups, one of which is provided with an overlapping ridge;

Fig. 2 illustrates the two semi-rigid hemispherical cups united toform a spherical gastight container;

Fig. 3 illustrates the spherical gas-tight container showing a convenient method of attachment of india rubber strips to form a rubber coating on its external surface;

Fig. 4 illustrates the spherical gas-tight container with one strip of rubber afiixed to its surface;

Fig. 5 illustrates a spherlcal gas-tight container coated with rubber and unvulcanized;

Fig. 6 illustrates a section of a rubber coated container after vulcanization; v

Figs. 7 and 8 illustrate a modification in which the spherical gas-tight container is composed of two cups joined together by means of a circular strip of the same or similar material as that of which the cups are formed;

Fig. 9 illustrates a ball in which the vulcanized spherical gas-tight container is covered with felt.

A is a tennis ball constructed from a thin hollow sphere B of semi-rigid character such as can be obtained from gutta percha or balata or a rubber mixture containing a pro portion of gutta percha and/or balata and inflated to the required degree by the provision therein of a suitable gas. The said hollow sphere B may be coated with a suitable layer of soft rubber laid on in the usual form of strips C, Figs. 3, 4 and 5, and after it has been vulcanized a suitable coating of felt may be applied to form the outer covering of the ball A. v

The hollow sphere B is preferably formed of two hemispherical cups b or it may be formed of two or more component parts comprising two cups. A suitable material from which to form the said component parts of the hollow sphere B is a prepared mixture containing Per cent by weight Purified balata Washed balata 15 Smoked sheet rubber Sulphur 10 Zinc oxide 20 will be found that both cups 6 and b have contracted together round the seam, glvmg from which all traces of grit or other foreign matter of similar character have been removed.

Such material suitably prepared is preferably moulded in the form of cups b b the cup 6 being of hemispherical shape, wh lst the cup 6 is of similar shape provided with an overlapping ridge 6; The cup 6 m.y be

provided with a suitable marking to indidistributed.

Although the complete spherical gas-tight container may be supplied with gas by injecting the same after vulcanization, to use a plugless ball inflated by the generation of gas produced from gas producing chemicals within it during the process of vulcanization. Satisfactory results are obtained by placing a mixture of 0.4 grammes of sodium nitrate and 0.4 grammes of ammonium chloride to which mixture three or four drops of water have been added in one of the cups b b the rims of which are cleaned with a petroleum spirit or other cleaning solvent and smeared with a solution of rubber dissolved in petroleum spirit and fitted and joined together.

The cups b 6 or component parts of the spherical container B, being of semi-rigid character are conveniently handled during the operations and very little skill on the part of the operative. is required to ensure accuracy of manipulationand perfect jointing.

The hollow spherical gas-tight container B thus formed is then allowed to stand until the rubber jointing solution is dry when it great resiliency. are extremely I prefer a satisfactory joint and producing a semirigid container on which to apply when desired a coating of soft rubber, and after vulcanization it will be found that the semirigidity of the container has disappeared and under the influence of the inflation gas has become extremely resilient.

In making the shells b b and after Vulcanizing the container B, it is necessary to thoroughly cool the moulds before the articles are removed therefrom.

This is specially important after vulcanization because the gas content is influenced by changes of temperature, and it is necessary to avoid unrestricted expansion of the gas contained therein under the influence of heat and the consequent production of oversized balls.

As above stated the gas container may before or after vulcanization be coated with a covering of rubber applied in any convenient manner when desired.

A suitable covering of felt or other material may be applied to the outer surface of the container when desired in any convenient manner. a

In Figs. 7 and 8 I have illustrated a modification in which the container is constructed of three component parts comprising two cups b 12 with an intermediate piece b.

Although I have described my invention as particularly applied to the manufacture of a tennis ball of my improved construction it will be obvious that my invention. is not limited thereto, and that it may be applied to the manufacture of any similar ball having a gas content.

Tennis balls constructed according to my invention and as herein described possess durable and ofler great resistance to wear. Moreover by their construction and the method thereof they can be manufactured by unskilled operatives so as to retain their inflation gas thus reducing to a minimum the very large proportion of rejects which has hitherto been The method of making tennis balls which comprises forming a relatively thin gas container made of two semi-rigid halves of a composition of rubber containing balata and vulcanizing materials, joining said halves with a gas tightjoint, applying relatively thick sheets of rubber over the container with their joints displaced relatively to the joint between said halves and vulcanizing and expending the assemblage.

In witness whereof, I have hereunto signed my name.

ALBERT ERNEST PEN FOLD. 

